U.S. Pat. No. 4,508,842 discloses a highly active vanadium containing catalyst capable of producing ethylene polymers having a broad molecular weight distribution. Said catalyst comprises:
(A) a solid catalyst precursor consisting essentially of
(1) an inorganic carrier, as support for PA1 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, and PA1 (3) a boron halide or alkyl-aluminum modifier, PA1 (1) a solid, particulate, porous, inorganic carrier, as support for PA1 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, and PA1 (3) a boron halide or alkyl-aluminum modifier, PA1 (1) a solid, particulate, porous, inorganic carrier, as support for PA1 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, PA1 (3) a boron halide or alkyl-aluminum modifier, and PA1 (4) a phosphorus containing molecular weight distribution (MWD) regulator having the formula (R).sub.3 P=0, wherein R is as defined above, PA1 (1) a solid, particulate, porous, inorganic carrier, as support for PA1 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, PA1 (3) a boron halide or alkylaluminum modifier, and PA1 (4) a phosphorus-containing molecular weight distribution (MWD) regulator having the formula (R).sub.3 P=0, wherein R is as defined above. PA1 M is boron or AlR.sup.2.sub.(3-a) wherein each R.sup.2 is an alkyl radical containing from 1 to 14 carbon atoms, which radicals may be the same or different, PA1 X is selected from the group consisting of fluorine, chlorine, bromine and iodine, and mixtures thereof, and PA1 a is an integer having a value of 0, 1 or 2, provided that a is 3 when M is boron. PA1 R is a monovalent hydrocarbon radical free of aliphatic unsaturation containing from 1 to 14 carbon atoms, or --OR.sup.1 wherein R.sup.1 is a monovalent hydrocarbon radical free of aliphatic unsaturation containing from 1 to 14 carbon atoms. PA1 (1) the reaction product of (a) a vanadium trihalide and (b) an electron donor, PA1 (2) a boron halide or alkyl-aluminum modifier, and PA1 (3) a phosphorus containing molecular weight distribution (MWD) regulator having the formula (R).sub.3 P=0, wherein R is as defined above. PA1 R.sup.4 is hydrogen or an unsubstituted or halosubstituted alkyl radical containing from 1 to 6 carbon atoms, which radicals may be the same or different, PA1 X' is halogen, and PA1 b is 0, 1 or 2.
(B) an alkylaluminum cocatalyst, and
(C) a halohydrocarbon polymerization promoter.
The polymers produced in accordance with U.S. Pat. No. 4,508,842 have a relatively broad molecular weight distribution, and excellent extrudability. These properties render them extremely useful in a wide variety of applications, such as wire and cable insulation, blow moldinq, film, and pipe fabrication. However, such polymers cannot be used in other applications, such as injection molding, which require a narrower molecular weight distribution.
U.S. Pat. No. 4,514,514, on the other hand, discloses a vanadium-containing catalyst useful in the preparation of ethylene polymers having a narrow molecular weight distribution. Such catalyst comprises:
(A) a solid catalyst component obtained by reacting a tetravalent or pentavalent vanadium halide compound, an organophosphorus compound and an organoaluminum compound.
(B) an organoaluminum cocatalyst, and
(C) a halocarbon polymerization activator.
While the catalysts prepared in this manner have been found useful in the preparation of polymers having a narrow molecular weight distribution, such catalysts do not exhibit high polymerization activity unless the vanadium halide compound, organophosphorus compound and organoaluminum compound employed to produce catalyst component (A) are reacted together under such conditions that catalyst component (A) is precipitated from solution as a particulate solid. Such procedure, however, results in the formation of irregularly shaped catalyst particles which are undesirable in continuous, commercial polymerization processes, particularly fluid bed polymerizations which require the use of rounded uniform catalyst particles in order to produce rounded polymer particles necessary to sustain polymerization. Rounded catalyst particles of uniform size are usually and conveniently prepared by impregnating the catalyst in a porous inorganic carrier, a procedure precluded by the catalyst preparation process of U.S. Pat. No. 4,514,514.
In addition to producing irregularly shaped catalyst particles, the catalyst preparation procedure of U.S. Pat. No. 4,514,514 requires the use of specific ratios of aluminum and phosphorus to effect precipitation of catalyst component (A) from solution. As a result, the relative amounts of aluminum, phosphorus and vanadium in the catalyst cannot be varied as desired. This inflexibility limits the use of the organoaluminum and organophosphorus compounds as catalyst modifiers and the ability to vary polymer properties through the use of these materials.
Japanese Patent Disclosure 61-138605, published June 26, 1986, is similar to U.S. Pat. No. 4,514,514 except that an organoaluminum compound is not employed in the preparation of the solid catalyst component. This patent disclosure does not describe the effect of the catalyst produced in accordance therewith on the molecular weight distribution of the polymers produced with it. However, as in U.S. Pat. No. 4,514,514, this disclosure requires precipitation of the solid catalyst component from solution and does not permit the use of catalyst supports impregnated with such catalysts.